Two-photon imaging can provide dynamic information about the behavior of cells within tissues including immune cells during infection and in response to cancer. Such information can provide unique insight into the course of events during infection and the impact of therapeutic treatments in vivo. Our existing 2- photon microscopy facility currently provides this important tool to a small group of investigators examining immune responses to intracellular pathogens, but is limited in terms of the number of fluorescent labels that can visualized and the number of projects and investigators that can be accommodated. We propose to expand our existing custom built 2-photon microscope by adding a second microscope with 5 detectors and more flexible scanning mechanism, and a second Ti Sa laser such that each scope can be operated with 2 lasers tuned to different excitation wavelengths. Our proposal will provide an extremely cost effective way to allow greater flexibility in imaging different fluorescent probes and to accommodate a greater number of users.